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Bad Outbound Sender in Microsoft O365

While using any mailing solution, we should always follow the best practices. Spamming and bulk emailing are not considered as best practices. One must avoid doing such things in the first place.

Bad Outbound Sender in Microsoft O365

Nowadays spamming and bulk emailing are global issues. These practices are followed by many people as per their requirements. Most of the emailing solutions do not support bulk emailing/spam but still, people are used to such practices.

It sometimes creates problem for the recipients as their mailboxes get flooded with unnecessary mails. In O365 if a user is sending spam or bulk mails regularly, then that particular user gets blocked from sending further mails but still can receive mails.


All such users are considered as bad outbound sender in O365. If they try to send more mails after getting blocked then they will get a non-delivery report( NDR)

stating that:

Server returns '550 5.1.8 bad outbound sender’

Unblocking bad outbound sender in O365

Once a user is restricted from sending further mails then you can revoke the restriction by performing the below steps:


  1. Go to the security & compliance center.

  1. Navigate to restricted users. For direct link check this -

  1. All the restricted users will be enlisted here. Select the particular user for which you want to revoke the restriction.

  1. Then select  Unblock

Powershell commands for unblocking sender

As we know,  there are multiple ways for doing a particular task in O365. The restricted
Users can also be unblocked using the below powershell commands.

1)  Get-BlockedSenderAddress : This command will display the list of the restricted users.

2) Remove-BlockedSenderAddress: This command will revoke the restriction from that user

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